The present invention relates to a needle assembly for collecting fluid such as from a patient, and more particularly, concerns a needle assembly for collecting multiple samples of fluid from a patient with an anti-backflow valve included in the assembly.
In the collection of fluids, and especially when such fluids may be blood or other bodily fluids from a patient, it is most desirable that backflow into the patient or other source be prevented. The reasons for prevention of fluid back into the patient are numerous. For example, when collecting blood into a collection container, various chemicals or other reagents may be present in the container for different tests on the blood sample. As the blood sample flows into this container, it mixes with the chemical therein. Should this mixture backflow into the patient, the chemical would then enter the patient's blood stream with potential harm to the patient. Another instance where backflow into the patient could be problematical involves clotting of the blood during the collection procedure. Should a small amount of the collected blood clot somewhere in the collection needle or container, backflow of such a clotted or coagulated amount of blood into the patient could cause serious difficulties. Accordingly, the inclusion of some type of anti-backflow device or valve into a needle assembly for the collection of fluids from a patient is a desired feature.
Attempts have been made previously to include such an anti-backflow valve in needle assemblies. These valves have been proposed in various shapes and forms, notably including shiftable ball valves, cup valves, disk valves with a self-sealing slit therein, and "duck bill" valves which open and close under differential fluid pressures. While, for instance, the ball valve is simple and straightforward to manufacture, there are problems inherent in the use of such a ball as a one-way valve. In particular, the mass of the ball generally takes a substantially large fluid differential in order to cause movement to open and close the valve. This is a shortcoming, especially when the pressures involved in the collection of the fluid sample may not be great. A ball valve for incorporation in a needle assembly is illustrated in U.S. Pat. No. 3,557,778. Some of the other aforementioned one-way valves suffer from a variety of deficiencies, both in structure and function. For instance, unless the one-way valve is reproducible from one valve to the next, it is difficult to predict accurately the pressures under which it will function. Thus, the inclusion of this type of valve in the needle assembly could produce unpredictable results. Moreover, some of the aforementioned valves are difficult to manufacture with concomitantly higher expense involved in their production and assembly into the needle structure. Accordingly, it can be seen that there is still room for improvement in anti-backflow valves which are used in multiple sample needle assemblies, particularly useful in obtaining blood samples from a patient.